Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

You can send an email to [email protected] if you have questions about how to use this forum.

Original Image vs Canvas Size re: Proportional Divider ?

edited October 2018 in Drawing
Good Morning, 
How do you determine, how large or small images will be on your canvas ? 
For example, If I have a Photo Frame that displays an apple orchard 12" x 12" and I want to paint this image on a much larger canvas say, 36" x 48" is there a formula for setting the proportional divider ? or does Linear Perspective take over ? I seem to have a natural ability to charcoal sketch a landscape, Profile of a model of a Statue, ( Rapturous Accent by Carlo Bronti 1951 ) but laying out a painting is a little different. Am I challenged by using multiple Horizons and Vanishing Points ? Or is there something I need to learn yet, that I haven't ?

I would like to just draw and use the methods from the The "Merode Altarpiece", attributed to the workshop of Robert Campin, c. 1427–32  

I have prepared my canvas, not sure what to paint on it yet, Iv'e studied it a couple times, and see different things, thought of a self portrait scene, where I am working on handmade clocks that I have made, tried to pencil sketch in my crazy ideas book, using one point perspective, struggling a bit with laying out the scene, which would be a combination of actual images still life ( my clocks, candle holders, coffee mugs etc ) and a Photograph of my self working at my bench, and some imagination as well. 

Currently working on several other oil paintings, including Starry Night on a 26" x 30" Canvas, Cherry Trees Holding The Moon, one abstract 30" x 40", and a imaginary abstract/realism Mountain Landscape 24" x 48", a few others.

Thank you


  • A proportional divider is typically not large enough to handle something 36" x 48", unless you made yourself a giant one.  It can only reach about 10" either side of your golden lines.

    With a large painting like that, use the grid method or a long ruler.

    But your example, of scaling a 12" x 12" to 36" x 48" means that with the large canvas not being square, you have to choose between cropping 3" off the small one, making it a 9" x 12", or imagining the content to paint in the extra foot of space on the large canvas.

    A proportional divider is not really a precision calibrated instrument, so getting that 3:1 ratio involves trial and error, and it's unlikely you'll get a perfect 3:1.  It depends where the holes are drilled.

    I cut my panel to have the same aspect ratio as the cropped reference, and do the rest with math.  In the rare event that the reference is the same size as the panel, I use a proportional divider, but just one side of it.
  • BOB73BOB73 -
    edited October 2018
    This sounds like a layout or grid question for @MikeDerby. He's a splinter artist like you and by his own words "I can't draw a bath but I can draft anything." Sorry I misspelled your name in the welcome. Believe it or not, people misspell my name too sometimes.
  • Ah the grid method, I know what it is but haven't tried it yet, thanks guys 
  • If you want to paint a big picture using a small reference photo and keep the same aspect ratio then the grid method works well.:)
  • @BOB73 - Bob I keep spelling your name backwards, oh here i go again bob,..
  • I tend to use grid method (on the one I posted here and one I'm working on at the moment). They are from photos A4 (painting same size). I have a cellophane A4 that I've drawn a grid on in indelible pen and tape that to the photo, then I draw the grid, lightly, on the gesso board I paint on.
    I have just received some A4 clear perspex that I ordered too for the same purpose.
  • @alsart it's not bob, boB or Bob it's 1301373. Bob73 is easier for people, especially the mathematically challenged.
  • I am challenged every way @BOB73 but none more so than with a brush in my hand,...
  • @RICCIO , a square image makes a square painting. Try cropping to get the aspect right.  A small image makes a fuzzy painting when enlarged that much unless you have the highest available pixel count.  Try roxy’s software to set up the composition. I use it fairly often.  One option is to blow the photo up and trace it. There is no such thing as cheating in art.  You can use a large grid with a proportional divider if you work from each line half way to the next one.  Then refine it within the grid.  12 to 36 is 1 to 3 so set your divider so it expands that much within a square.  It’s important that your reference photo have the lines added to it before you print so they remain fixed throughout.  
    Pit sounds really ambitious.  Good luck.  I look forward to seeing it.
  • Riccio, thanks for posting on my wall. The "Splinter Artist" remark was regarding the fact that both you and Mike Derby are Wood workers. Assuming you are both familiar with layout tools and measuring, I thought it would be best to answer your request. I know from his previous posts he has developed some expertise in maintaining aspect ratio when enlarging or reducing transfers.
  • Folks

    Maintaining an aspect ratio is a snap. Draw a line corner to corner through the source image and any support touching the extended line will have the same aspect ratio.


  • Wouldnt there need to be some kind of measurement along the horizontal and vertical sides  ?
  • thought you could avoid math becoming an artist, didn't you?! HAH! 
  • @dencal     Denis, you will never believe this, but I already know this!!!!!!!!!!!!!!!!!!!!!   This will be the only conversation of this nature we will ever have, I am sure.
  • Good Evening Everyone, 
    I have a question on grid layout, 

    Ok trying the grid method, not enjoying it so far, may be possible I'm doing something wrong. 
    Any suggestions would be welcome, 
    My Image is small, 12" wide 7" Tall the canvas is 40"wide and 30"tall
    so:   40/30 divided by 12/7 equals 3.33 and 4.28  So I made 1" on the photo equal 3.33  (3 1/4" )
    (horizontal )and 4.28 (4 1/4" ) ( Vertical ) 
    Is this the correct math in laying out the grid lines ?
    It seems I am better at drawing with charcoal free hand than trying force things to fit in little boxes.

  • Hello Dencal, 
    I dont know what this means, could you explain a little more?
    Do I need to know the aspect ration of the source image first, ?
    Thank You

    dencal said:

    Maintaining an aspect ratio is a snap. Draw a line corner to corner through the source image and any support touching the extended line will have the same aspect ratio.



    Sure. Keeping an aspect ratio true between a source and destination image is all about maintaining the relationship between length and breadth as the image grows or shrinks.

    So to maintain an original image 12x7 aspect ratio to a larger canvas size say, 3.3 times bigger is 40x23.1.
    If you wanted iarger try multiplying bot sides by an enlargement factor of say, five. This will need a canvas measuring 60x35.

    Grids are a separate consideration depending on complexity of subject matter. Six by eight squares is sufficient for broad scale accuracy, perspective and proportion. If more detail is needed a sub-divided square or plotting with proportional dividers works well.

    I much prefer a lattice grid to the rectangular version. Here is an example.

    No measurement needed, automatic scaling and infinitely divisible.

    Best of all is freehand drawing to build skill and confidence. This is why I go to life drawing classes.


  • Thank you very much, Denis !

Sign In or Register to comment.